Organic trithiophosphites as rocket propellants



Dec. 4, 1962 D. R. CARMODY ETAL 3,066,478

ORGANIC TRITHIOPHOSPHITES AS ROCKET PROPELLANTS Filed NOV. 50, 1951 OXlD-IZER INVENTORS. DON R. CARMODY ALEX ZLETZ ATTOR EY.

3,06%,478 ORGANIC TRTTHTOPHQSPHITES AS ROCKET PRGPELLANTS Don R. Carrnody, Crete, and Alex Zletz, Chicago Heights, lih, assignors to Standard Gil Company,

Chicago, Ill., a corporation of Indiana Filed Nov. 30, 1951, Ser. No. 259,034 15 Claims. (Cl. oil-35.4)

This invention relates to reaction propulsion. More particularly, it relates to novel fuels that are spontaneously combustible, when contacted with an oxidizer, for the generation of hot gases in a rocket motor.

Rocket propulsion is now being used to assist airplanes in takeoff or to attain bursts of speed in excess of that attainable with the regular power plant. Also rocket propulsion is being used in the military projectile field, wherein an explosive container is air-borne by means of an attached rocket motor; these projectiles may be launched from the earths surface or from an airplane in flight.

Rocket fuels, now in use, are either a single self-contained fuelmonpr0pellantwhich may be either a solid or a liquid; or a separate fuel and a separate oxidizer bipropellant. The bipropellant fuels are stored in separate tanks outside the rocket motor itself. The solid monopropellant fuels are stored in the combustion chamber of the rocket motor. The bipropellant rocket motor consists of a suitable combustion chamber provided with one or more pairs of nozzles adapted .to inject therein the fuel and the oxidizer, separately and simultaneously. The combustion of the fuel and the decomposition of the oxidizer creates mass of hot, burning gases which are ejected at high velocity through a suitable orifice; the reaction from this ejection provides the propulsive force. In general, the bipropellant rocket motor is more amenable to control and uses a somewhat more economical combustion chamber.

The ignition reaction between the fuel and the oxidizer may be initiated by an electric spark, a hot wire, a hot surface or may be spontaneous. A spontaneous combustion or self-ignition is preferred because of the possibilities of electrical and mechanical failure of the spark and hot surface methods of ignition. A fuel which is self-igniting when contacted with an oxidizer is called a hypergolic material.

Many materials which are hypergolic at temperatures at about +75 F. lose this property when the temperature is lowered. The temperature at the earths surface may vary from a high of about +l20 F. to a low of 40 F., and in the polar and sub-polar regions, to as much as 70 F. The temperature of liquids stored in ordinary tanks exposed to the sun may reach as much as +150 F. The temperatures encountered by airplanes at high altitude are often as low as 70 F. and, may be lower than -100 F. Thus a rocket motor using a hypegolic fuel may have to be started into operation With the fuel and oxidizer at a temperature as low as, or possibly lower than, -70 F. In this specification, the term atmospheric temperatures includes the entire range between about +120 F. to about -100 F.

The walls of the combustion chamber become very hot from the heat of the burning gases generated by the reaction of the fuel and the oxidizer. This hot surface, and the mass of hot gases in the chamber, has a pronounced favorable effect on the self-ignition characteristics of the fuel and oxidizer. Many fuels which are non-hypergolic at the temperature existing in the fuel tank of the rocket unit are rapidly hypergolic in the extremely hot combustion chamber. For economy of operation, a fuel that is hypergolic at very low temperatures may 3,956,478 Patented Dec. 4, 1962 be used to initiate the combustion in and to start the cold reaction motor; the use of this starter fuel may be continued until the hot gases generated have heated the combustion chamber to a high temperature; at this point the flow of the starter fuel can be stopped and a cheaper, although nct as highly hypergolic or even a non-hypergolic fuel can be utilized for the continuous operation of the reaction motor.

An object of this invention is to provide a reaction propulsion method using a novel hypergolic fuel. Another obejct is to provide a novel hypergolic fuel containing appreciable amounts of essentially non-hypergolic hydrocarbons for use in rocket motors. Still another object is to provide a novel hypcrgolic fuel that is relatively insensitive to atmospheric temperature changes. Yet another object is to provide a hypergolic fuel for reaction propulsion that is relatively cheap and can be made available in abundant supply. A particular object is to provide a fuel for initiating combustion in a reaction-type motor at atmospheric temperatures.

Very briefly, the novel hyp-ergolic fuel of this invention consists of an organic trithiophosphite of the empirical formula RR'RS P wherein: P represents the element phosphorous, S represents the element sulfur and R, R and R" represent the same or different hydrocarbon radicals selected from the group consisting of: aliphatic radicals containing 1 to 8 carbon atoms, cycloaliphatic radicals containing not more than 8 carbon atoms, and monocyclic aromatic radicals containing not more than 4 substituent carbon atoms. A novel hypergolic mixed fuel is made by mixing the above defined organic trithiophosphite with an essentially non-hypergolic hydrocarbon in proportions that will be defined later in this specification.

The oxidizers of this invention are: The most commonly used material is white fuming nitric acid-abbreviated WFNA-which normally contains less than about 2 weight percent of water. More dilute solutions have been utilized by fortifying the acid with nitrogen tetroxide-N O Red fuming nitric acid-RFNA-normally contains less than about 5% of Water and between about 5 and 20% of N 0 Nitric acid containing about 30% of water can be used with some of the organic thiophosphites; although such a dilute acid is not of practical significance in rocket propulsion. Favorable results are obtained with most of the organic thiophosphites when using nitric acid containing about 20% of water. Sodium and potassium nitrites and sodium and potassium nitrates are often added to WFNA to depress the freezing point; usually an aqueous solution of the salt is used. Thus WFNA plus 4% of potassium nitrate and 4% of water has a freezing point of about F. Liquid nitrogen tetroxide is an excellent oxidizer when used above its freezing point. A very satisfactory oxidizer for use at temperatures as low as -6(; F. consists of a mixture of N 0 and nitrous oxide, as described in U.S. 2,403,932. An excellent oxidizer is obtained by adding 10 to 30% of sulfuric acid monohydrate (H 50 or about 1 to 30% of oleum to strong nitric acid. The particularly effective nitric acid oxidizers contain not more than about 10 weight percent of non-acidic material, such as, water or aqueous potassium nitrate solution. The preferred oxidizers are white fuming nitric acid, red fuming nitric acid, and nitric acid-oleum mixtures. The use of the general term "nitric acid oxidizer in this specification and in the claims is intended to include all the favorable compositions described in this paragraph.

It has been discovered that certain organic trithiophosphites have hypergolic properties at temperatures below about +l20 F. Evidence has been found that, at least among those compounds that are within the scope of the invention, the empirical composition consists essentially of 3 an equilibrium of two isomers having the structural formulas:

RS-P

and

R RS-I SR g Infra-red analysis indicates that the trivalent phosphorous compound is the predominant constituent of the equilibrium mixture. The term trithiophosphite as used in this specification and in the claims includes both the substantially pure trivalent phosphorous compounds and mixtures of the triand pentavalent phosphorous compounds, wherein the trivalent form is the predominant constituent. The symbol R in the above structural formulas represents the same or different hydrocarbon radicals selected from the group cOnsisting of: aliphatic radicals containing 1 to 8 carbon atoms, cycloaliphatic radicals containing 8 or less carbon atoms, and monocyclic aromatic radicals containing 4 or less substituent carbon atoms. The term aliphatic is intended to include radicals that contain one or more unsaturated linkages as well as the alkyl radicals. The term cyclolaiiphatic is intended to include not only the cyclic radicals containing 3 or more carbon atoms in the ring but also substituted rings and also includes the presence of unsaturated linkages in the ring and/or in a side chain. The term monocyclic aromatic is intended to include the phenyl radical and also substituted phenyl radicals and also includes the presence of unsaturated linkages in a side chain. In the case of the ring compounds, it is intended to include the compounds wherein the sulfur is linked either to a ring carbon atom or to a substituent or side-chain carbon atom.

More effective as hypergolic fuels are the organic trithiophosphites wherein, R represents the same or dilferent hydrocarbon radicals selected from the group consisting of: alkyl radicals containing 1 to 4 carbon atoms, unsaturated aliphatic radicals containing 2 to 8 carbon atoms, cycloalkyl radicals containing 3 to 4 carbon atoms, unsaturated cycloaliphatic radicals containing 3 to 8 carbon atoms, and the aromatic radicals phenyl, tolyl, xylyl, ethylphenyl and vinylphenyl.

For operation within the entire range of atmospheric temperatures, an extremely effective hypergolic fuel consists of a mixture of trialkyl trithiophosphites which contain methyl, ethyl, propyl and butyl radicals or mixtures thereof and wherein the methyl and ethyl groups are the predominant radicals. The preferred hypergolic fuel for atmospheric temperature operation consists essentially of trimethyl trithiophosphite, or triethyl trithiophosphite or a mixture thereof.

The organic trithiophosphites are, in general, heavy, clear, mobile, high boiling liquids, with a garlic-like odor. They are fairly stable when exposed to elevated temperatures; for example, a triethyl trithiophosphite was held at 410 F. for 4 hours, in the absence of free-oxygen, before an orange precipitate formed in the liquid; however, the resultant liquid was still superior in hypergolic activity. They are quite stable to the action of water; for example, a mixed trialkyl trithiophosphite was steam distilled Without any decomposition and another sample was held in contact with water for four weeks at 80 F. without deleterious etfect. Stainless steel is not affected by contact with these organic thiophosphites at ambient temperatures. They are miscible with hydrocarbons and most of the common organic solvents. However, they are susceptible to oxidation by free-oxygen and are rapidly converted at elevated temperatures to non-hypergolic materials.

The organic trithiophosphites of this invention can be made by the reaction of a mercaptan and phosphorous tri- A. chloride as describedby l ippert andR eid in I. Am. Chem. Soc., 60, 2370 (1938) or, preferably, by the reaction of a disulfide and yellow phosphorous as described in U.S. 2,542,370. The products from these methods of preparation contain minor amounts of impurities, as evidenced by infrared analysis.

The trialkyl trithiophosphites are particularly suitable hypergolic fuels for rocket propulsion because of their very low freezing points, high boiling points, and comparatively small increase in viscosity with decrease in temperature. Not only do they have very low freezin points but also they have a great tendency to supercool, i.e., remain liquid at temperatures below the true freezing point. Many of the trialkyl trithiophosphites can be held for considerable periods in the liquid state at temperatures below -lO5 F.; these supercooled liquids are difiicultly crystalizaole even when seeded with small crystals of the trialkyl trithiophosphite. The presence of minor amounts of impurities, formed in the preparation of the trialkyl trithiophosphite, is beneficial in that the freezing point is depressed; thus these impure trialkyl trithiophosphites have freezing points below -l00 F.; there is no noticeable difference in hypergolic activity of these compounds containing minor amounts of impurities and the pure compounds. Those fuels which contain minor amounts of impurities from side reactions in the preparation of the organic trithiophosphite are included within the scope of the invention.

Certain physical properties of the more readily available trialkyl trithiophosphites are listed below. The listed compounds were made by the method of U.S. 2,542,370, since this method gives excellent yields of good purity material. Two mixed compositions were made by reacting, according to the method of U.S. 2,542,370, mixtures of disulfides obtained from petroleum naphthas: the composition designated C C was made from a natural mixture of disulfides containing methyl, ethyl and some propyl groups; the composition designated TP was made from a mixture of disulfides that was derived by the oxidation of a natural mixture of mercaptans having the approximate composition: methyl, 25 mol percent; ethyl, 45%; propyl, 25%; and butyl, 5%. The other compounds were made from the corresponding substantially pure disulfides.

Alkyl Radical Specific B.P. (1 F.P., F.

Gravity mm. Hg),

Viscosity, Oentistokes Temperature, F.

TETP TP 1 supercooled.

The organic trithiophosphites wherein the hydrocarbon radical is aryl in nature, such as, phenyl, tolyl, or xylyl, are good hypergolic fuels at moderately low temperatures.

They do not possess the viscosity characteristics of the alkyl trithiophosphites and become thick, syrupy liquids at temperatures well above their freezing points. Thus tritolyl trithiophosphite becomes relatively ineffective as a hypergolie fuel at about 0 F., because the viscosity is so great that the liquid does not flow.

The ignition characteristics of fuels were studied using a drop test method. This method utilizes a test tube, 1 in. x 4 in., containing 1 ml. of oxidizer. The fuel is added dropwise into the test tube by means of a syringe calibrated in 0.01 ml. markings. Usually 0.1 ml. of fuel is added per test; however, the feed usage may vary between 0.01 and 0.2 ml. per ml. of oxidizer. Low temperature tests were carried out by cooling the test tube and the oxidizer contained therein to the desired temperature by means of a Dry Ice-chloroform bath; a drying tube inserted into the top of the test tube excluded moisture. The fuel was cooled separately to the desired temperature. By supercooling, it was possible to carry out tests at temperatures below the freezing point of the fuel and of the oxidizer. The time elapsing between the addition of the fuel to the oxidizer and ignition thereof-the ignition delay-was determined visually as either: extremely short, very short, short and ignition. An extremely short ignition delay corresponds to substantially instantaneous ignition.

In order to measure more accurately the amount of fuel added and also to approach more closely a reproducible degree of mixing, a capillary tube test was also used. A capillary tube of 2 mm. diameter or less, with a syringe attached at one end, is filled with a measured amount of fuel undergoing the test; an air space is left at the end of the tube. The capillary tube is inserted into the oxidizer in a beaker and the fuel is injected into the acid by depressing the syringe plunger. By this capillary tube method, amounts of fuel on the order of 0.0002 ml. can be added to the oxidizer.

The following tests illustrate the hypergolic activity of some of the organic trithiop-hosphites and of other hypergolic fuels.

Test 1 This series of runs used WFNA, containing 2 wt. percent of water, as the oxidizer. The minimum hypergolic temperature and visual ignition delay for each compound were determined when using 0.1 ml. or less of compound per ml. of acid in the drop test. Temperatures below --49 F. were obtained by supercooling the acid.

Test 2 This series of runs was made in the capillary tube method at }75 F. to determine the minimum volume of fuel required for the ignition, with 100/ml. of WFNA as oxidizer.

Compound: Minimum volume ml. Furfuryl alcohol 0.006 Isobutyl mercaptan .009 Ethyl disulfide .011 Aniline .025

Triethyl trithiophosphite .00O2

6 T est 3 In this test, fuming nitric acid was the oxidizer. The minimum hypergolic temperature and an ignition delay for TETP and TP were determined when using 0.05 ml. of fuel in the drop method. At a temperature of F., both fuels ignited after an extremely short delay.

Test 4 In this test, WFNA plus 4% of potassium nitrate and 4% of water was contacted with TETP and TP in the drop method. At a temperature of 95 F., both fuels ignited after an extremely short delay.

T est 5 In this test, 70% nitric acid was the oxidizer. In the drop method, TETP ignited at a temperature of +75 F. However, TP did not ignite at this temperature, although a vigorous reaction took place.

Test 6 In this test, liquid nitrogen tetroxide was used as the oxidizer. This is a difliculty decomposible oxidizer and represents a severe test of the hypergolic activity of a fuel.

Compound: Hypergolic temperature F. Trimethyl trithiophosphite +l3 1 Triethyl trithiophosphite About +60 Furfuryl alcohol No ignition Aniline +13 1 supercooled solid N204.

It has been found that hydrocarbons which are essentially non-hypergolic even at temperatures above +120 F. can be mixed with the organic trithiophosphites to obtain a fuel that is hypergolic with nitric acid oxidizer. The essentially non-hypergolic hydrocarbon should have a low freezing point, on the order of 70 F., in order to obtain a low temperature hypergolic mixed fuel. The boiling point of the essentially non-hypergolic hydrocarbon has an effect on the ignition temperature of the mixed fuel; a non-hypergolic hydrocarbon with a maximum boiling point below about 600 F. is preferred.

The composition of the mixed hypergolic fuel is dependent primarily upon the particular nitric acid oxidizer being used and, below about 0 F., the composition of the mixed fuel, which is still hypergolic, is substantially independent of temperature. When using nitric acid containing less than about 5% of water as the oxidizer, such as, WFNA or RFNA, as much as 40 volumes of non-hypergolic hydrocarbon can be present in volumes of the mixed fuel; this mixed fuel is hypergolic, with an extremely short ignition time, at atmospheric temperatures. Above about 0 F., the amount of non-hypergolic hydrocarbon tolerable in the mixed fuel increases with increase in temperature. At 75 F., the mixed fuel may contain about 60 volume percent of non-hyperbolic hydrocarbon, when using nitric acid containing less than about 5% of water. The tolerance for non-hypergolic hydrocarbon in the mixed fuel is decerased with increase in non-acidic content of the nitric acid. For example, a mixture of only 30 volumes of non-hypergolic hydrocarbon and 70 volumes of TP is rapidly hypergolic at 92 F. when the oxidizer is either 90% fuming nitric acid or WFNA plus 4% of KNO and 4% of water.

The presence of a low freezing point hydrocarbon improves the usefulness of triaryl trithiophosphites as the mixture of low freezing point hydrocarbon and triaryl trithiophosphite is more fluid at low temperatures than the triaryl trithiophosphite itself. There appears to be no significant difference in hypergolic activity of mixtures of a non-hypergolic hydrocarbon with the various lower molecular weight organic trithiophosphites.

Certain hydrocarbons, such as, shale oil fractions, some olefins, etc. are highly reactive or even hypergolic to some extent with the oxidizer. A low-temperature hypergolic mixed fuel can be made with these hydrocarbons, which mixed fuel can contain less of the trithi'ophosphite than a mixed fuel containing essentially non-hypergolic hydrocarbons. Such mixed fuels are within the scope of the invention.

Tests were made to determine the effect of the admixture With certain organic trithiophosphites, of hydrocarbons that are non-hypergolic at about +75 F. with WFNA. Some examples of these tests are given below.

Test 7 Several non-hypergolic hydrocarbons were run at +75 F. using WFNA as the oxidizer and TETP as the hypergolic component of the mixed fuel. The maximum amount, in volume percent of mixed fuel, of the nonhypergolic hydrocarbon that could be added before the hypergolic activity in the drop method decreased to an undesirably long ignition time, is listed below for several compounds.

Hydro- Maximum Hydrocarbon carbon, Amount B.P., F. Allowable Toluene. 232 50 5O 50 40 60 1 Hydrocarbon J is a mixed petroleum distillate having an end point of about 525 F. and a Reid vapor pressure of about 6 pounds.

Test 8 The effect of temperature upon tolerable dilution of a hypergolic mixed fuel was determined in this test using the drop method. The oxidizer was WFNA, the hypergolic component was TP, and the non-hypergolic hydrocarbon was J-fuel. The results of this test are shown 1 supercooled.

Test 9 Test 7 was repeated using as oxidizer, 98% fuming nitric acid, in one series, and WFNA plus 4 wt. percent of KNO and 4 wt. percent of water, in another series. Within the limits of experimental error, the ignition performance of the two oxidizers were identical. The results are listed below.

Vol. percent J-fuel Hypergolic temperature, F.: tolerable This invention is particularly advantageous when the fuel, oxidizer and combustion chamber are initia lly at atmospheric temperature as combustion begins Without auxiliary ignition devices or without preheating of the combustion chamber. The nitric acid oxidizer and the fuel should be added to the combustion chamber separately and simultaneously so as to contact each other with considerable intermingling action. Usually the relative amounts of the two materials will be somewhat in excess of the theoretical oxygen balance ratio of 0x1- dizer to fuel. When using the hypergolic fuels of this invention about 3.5 to pounds of WFNA are injected per pound of the fuel. While it is possible to vary the ratio during operation, it is preferred to maintain a constant ratio.

By way of example, this invention is applied to the driving of an airto-air missile. The figure shows a schematic layout of the combustion chamber and bipropellant feed system of a reaction motor, such as is used in a military rocket projectile. In the figure, vessel 11 contains a quantity of inert gas under high pressure; nitrogen or helium is a suitable gas. Helium is passed through line 12, through a regulatory valve 13 which passes the helium into line 14 at a constant pressure. From line 14, the helium is passed into line 16 which is connected to the vessels containing the fuel and the oxidizer. Vessel 17 contains the oxidizer; the pressure of the helium from line 16 forces the oxidizer through line 18, through solenoid actuated throttling valve 21, through line 23, and through nozzle 24 into combustion chamber 26. Combustion chamber 26 is provided with a nozzle 28. Vessel 31 contains the main supply of fuel. The helium pressure forces the fuel out of vessel 31 through line 32, through solenoid actuated valve 33, and through line 35 to vessel 37. Vessel 37 may be used to contain a special starter fuel or an additional amount of the main fuel. The pressure in line 36 forces the contents of vessel 37 through line 38, through solenoid actuated throttling valve 41, through line 43 and through nozzle 44 into combustion chamber 26. The nozzles 24 and 44 are so arranged that the streams of liquid violently impinge and thoroughly intermingle and ignite. The combustion of the fuel and the oxidizer results in the generation of a large volume of very hot gases which pass out of the combustion chamber through orifice 23; the reaction from this expulsion of gases drives the rocket.

For ordinary velocity operations, only one fuel is used, herein T1 is used, and both vessels 31 and 37 will contain TP and valve 33 will be in the open position. The oxidizer is a mixture of WFNA and 8% of a 50% solution of KNO in water. This oxidizer is used because it is liquid at about -70 F. temperature which the oxidizer and fuel will attain while being carried at high altitude by an aircraft looking for a target. The missile is launched by activating the solenoids on valves 21 and 41. The oxidizer and the TF fuel are forced into the combustion chamber in the weight ratio of 4.5 to l. Instantly combustion takes place and the missile hurtles toward the target.

For some operations, very high velocities are necessary, which velocities can be reached only by using a very high thrust fuel. An air-to-air missile usually has a relatively short combustion chamber and this fact limits the fuels that can be used for high thrust operation. Turpentine is an excellent high thrust fuel for this use. The turpentine is stored in vessel 31 and valve 33 is closed. About 4 lbs. of oxidizerWFNA plus 8% of KNO and waterare used per lb. of turpentine. Trimethyl trithiophosphite is used as the starter fuel and is stored in vessel 37. Only enough starter fuel to heat up the combustion chamber is needed; in this case 0.1 second of operation or less. The missile is launched by activating the solenoids in valves 21, 33 and 41. The turpentine forces the trimethyl trithiophosphite into the combustion chamber where the oxidizer and trimethyl trithiophosphite ignite and heat up the chamber. Without interruption, the turpentine follows into the heated chamber and burns to give the very high thrust reaction.

We claim:

1. A rocket propulsion method, which method comprises injecting separately and simultaneously into the combustion chamber of a rocket motor (a) a fuel consisting essentially of an organic trithiophosphite having the empirical formula, R 8 1 wherein: P represents the element phosphorous, 8 represents the element sulfur and R represents an alkyl radical containing not more than 4 carbon atoms, and (b) a nitric acid oxidizer which contains not more than about 20 weight percent of nonacidic materials, in an amount and at a rate suflicient to initiate a hypergolic reaction with and to support combustion of the fuel.

2. The method of claim 1 wherein said oxidizer is white fuming nitric acid.

3. The method of claim 1 wherein said oxidizer is red fuming nitric acid.

4. The method of claim 1 wherein said fuel is trimethyl trithiophosphite.

5. The method of claim 1 wherein said fuel is triethyl trithiophosphite.

6. The method of claim 1 wherein said fuel is tri-nbutyl trithiophosphite.

7. A method of initiating combustion in a rocket motor, which method comprises injecting separately and simultaneously into the combustion chamber of the rocket motor trimethyl trithiophosphite and red fuming nitric acid, in an amount and at a rate sufiicient to initiate a hypergolic reaction with and to support combustion of the thiophosphite.

8. A method of initiating combustion in a rocket motor, which method comprises injecting separately and simultaneously into the combustion chamber of the rocket motor triethyl trithiophosphite and red fuming nitric acid, in an amount and at a rate sufficient to initiate a hypergolic reaction with and to support combustion of the thiophosphite.

9. A rocket propulsion method which comprises injecting separately and simultaneously into the combustion chamber of the rocket motor trimethyl trithiophosphite and liquid nitrogen tetroxide, in an amount and at a rate sufficient to initiate a hypergolic reaction with and to support combustion of the thiophosphite.

10. A rocket propulsion method, which comprises injecting separately and simultaneously into the combustion chamber of a rocket motor (1) a hypergolic mixed fuel consisting of (a) a liquid, hydrocarbon boiling below about 600 F., said hydrocarbon being characterized by the absence of hypergolic reaction when contacted, at about +75 F., with about volumes of white fuming nitric acid per volume of said hydrocarbon, and (b) an organic trithiophosphite having the empirical formula R S P wherein: P is phosphorus, S is sulfur and R is an alkyl radical containing not more than 4 carbon atoms, and (2) a nitric acid oxidizer containing not more than 20 weight percent of non-acidic materials, in an amount and at a rate sufficient to initiate a hypergolie reaction and to support combustion of the mixed fuel.

11. The process of claim 10 wherein said hydrocarbon is toluene.

12. The process of claim 10 wherein said hydrocarbon is iso-octane.

13. The process of claim 10 wherein said hydrocarbon is a liquid petroleum distillate having an ASTM endpoint of about 525 F. and an RVP of about 6 p.s.i.

14. A rocket propulsion method which comprises injecting separately and simultaneously into the combustion chamber of a rocket motor (1) a hypergolic mixed fuel consisting of (a) about 40 volume percent of a liquid petroleum distillate having an ASTM endpoint of about 525 F. and an RVP of about 6 p.s.i., said distillate being characterized by the absence of hypergolic reaction when contacted, at about F., with about 10 volumes of white fuming nitric acid per volume of said distillate, and (b) the remainder essentially trimethyl trithiophosphite and (2) white fuming nitric acid in an amount and at a rate sufficient to initiate a hypergolie reaction and to support combustion of the mixed fuel.

15. A rocket propulsion method, which method comprises injecting separately and simultaneously into the combustion chamber of a rocket motor a fuel consisting of a trialkyl trithiophosphite containing from 1 to 4 carbon atoms in each alkyl group and an oxidizing agent consisting of concentrated nitric acid, in an amount and at a rate suflicient to initiate a hypergolic reaction with and to support combustion of the fuel.

References Cited in the file of this patent UNITED STATES PATENTS 2,261,227 Cloud Nov. 14, 1941 2,382,905 Pedersen et al. Aug. 14, 1945 2,542,370 Stevens et al. Feb. 20, 1951 2,552,570 McNab et al. May 15, 1951 2,573,471 Malina et al. Oct. 30, 1951 OTHER REFERENCES Journal of the American Rocket Society, No. 72, December 1947, pages 17, 32-35 inclusive.

Killeffer: Fuels for Jets, in Scientific American, September 1945, page 163.

Lippert et al.: J. Am. Chem. Soc., vol. 60, page 2370 (1938).

t. t in up 

1. A ROCKET PROPULSION METHOD, WHICH METHOD COMPRISES INJECTING SEPARATELY AND SIMULTANEOUSLY INTO THEHE COMBUSTION CHAMBER OF A ROCKET MOTOR (A) A FUEL CONSISTING ESSENTIALLY OF AN ORGANIC TRITHIOPHOSPHITE HAVING THE EMPIRICAL FORMULA, R3S3P WHEREIN: P REPRESENTS THE ELEMENT PHOSPHOROUS, S REPRESENTS THE ELEMENT SULFUR AND R REPRESENTS AN ALKYL RADICAL CONTAINING NOT MORE THAN 4 CARBON ATOMS, AND (B) A NITRIC ACID OXIDIZER WHICH CONTAINS NOT MORE THAN ABOUT 20 WEIGHT PRECENT OF NONACIDIC MATERIALS, IN AN AMOUNT AND AT A RATE SUFFICIENT TO INITIATE A HYPERGOLIC REACTION WITH AND TO SUPPORT COMBUSTION OF THE FUEL. 